Video image data is frequently generated in an interlaced format and then converted into a higher density noninterlaced format that is compatible with progressive displays (e.g., computer displays, HDTVs). In the interlaced format, each frame of video data containing a two-dimensional array of pixels includes an even field of data and an odd field of data that are typically sequentially generated in a repeating even-odd sequence of fields. The even field of data includes pixels located on even-numbered scan lines within the frame and the odd field of data includes pixels located on odd-numbered scan lines within the frame.
In contrast, in the noninterlaced format, which is frequently referred to as a progressive scan format, each video image is represented by a single frame that includes pixels on both even and odd scan lines. Accordingly, deinterlacing techniques to convert video data from an interlaced format to a progressive scan format typically involve operations to double the number of active scan lines. Two fundamental deinterlacing techniques include video mode deinterlacing and film mode deinterlacing. Video mode deinterlacing includes interfield processing and intrafield processing. The simplest method of generating additional scan lines during video mode deinterlacing includes intrafield processing using only information from each field being processed. One of these methods is referred to as scan line duplication, which does not operate to increase vertical resolution within a resulting frame of data. In scan line duplication, each scan line to be generated simply duplicates a prior active scan line. This means that with respect to an odd field of data, each even scan line 2, 4, 6, 8, . . . to be generated is merely a duplicate of a corresponding odd scan line 1, 3, 5, 7, . . . . Similarly, with respect to an even field of data, each odd scan line 1, 3, 5, 7, . . . to be generated is merely a duplicate of a corresponding even scan line 2, 4, 6, 8, . . . . Another method using intrafield processing is referred to as scan line interpolation, which generates interpolated scan lines between the original active scan lines. The simplest implementation of scan line interpolation uses linear interpolation to generate each added scan line as an average of an immediately adjacent upper active scan line and an immediately adjacent lower active scan line.
One of the simplest methods of generating additional scan lines using interfield processing includes field merging. This technique merges two consecutive fields together to produce each frame of video data. In particular, the active scan lines associated with each field of video data are combined with the active scan lines associated with an immediately previous field of video data to thereby yield a sequence of frames at a frame rate equivalent to the rate at which the original fields of video data are generated. Using this method, the vertical resolution of each frame of data is doubled only in regions of no movement. However, moving objects within each generated frame of data will typically have artifacts (e.g., double images) caused by the time difference between each pair of fields used to generate a corresponding frame.
To address this problem of artifacts, motion adaptive deinterlacing techniques have been developed. One such technique is disclosed in U.S. patent Publication No. 2005/0270417 to Jiang et al., entitled “Deinterlacing Video Images with Slope Detection.” In particular, Jiang et al. discloses a video image deinterlacer having a slope protection system therein that determines directions (i.e., slopes) for diagonal lines along an edge of an object being displayed. A similar technique is also disclosed in U.S. patent Publication No. 2005/0168633 to Neuman et al., entitled “Method and System for Motion Adaptive Deinterlacer with Integrated Directional Filter.” In particular, Neuman et al. disclose a method for detecting an edge in an image and determining a direction of the edge. A filter is then selected using the direction of the edge in the image and a spatial average of the edge in the image is produced using the selected filter.